Heatable or coolable roller

ABSTRACT

This invention relates to a heatable or coolable roller which comprises a hollow cylindrical exterior shell, at least one hollow cylindrical interior shell secured to the exterior shell and having aperture means therein adjacent each end thereof, flow-causing means on the exterior of the interior shell for causing flow of a heat transfer medium, and means for introducing heat transfer medium into said roller and discharging said medium from said roller.

United States Patent Inventor Hermann Trautner Niederwalluf, Rheingau, Germany Appl. No. 847,664 Filed Aug. 5, 1969 Patented Oct. 12, 1971 Assignee Kalle Aktiengesellschaft Wiesbaden-Biebrich, Germany Priority Aug. 6, 1968 Germany P 17 75 394.5

HEATABLE OR COOLABLE ROLLER l 1 Claims, 5 Drawing Figs.

US. Cl. 165/90 Int. Cl F28g 5/02 Field of Search 165/89, 90, 80; 34/135, 136

[56] References Cited UNITED STATES PATENTS 2,696,635 12/1954 Rehak et al 165/89 X 2,919,904 l/1960 Cundif 165/89 2,956,348 10/1960 Mueller 165/89 X 3,208,513 9/1965 Pendleton 165/90 Primary Examiner-Frederick L. Matteson Assistant Examiner-Theophil W. Streule Attorney-James E. Bryan ABSTRACT: This invention relates to a heatable or coolable roller which comprises a hollow cylindrical exterior shell, at least one hollow cylindrical interior shell secured to the exterior shell and having aperture means therein adjacent each end thereof, flow-causing means on the exterior of the interior shell for causing flow of a heat transfer medium, and means for introducing heat transfer medium into said roller and discharging said medium from said roller.

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ATTORNEYS HEATABLE on COOL ABLE ROLLER This invention relates to a roller, heatable or coolable by means of liquids or condensable vapors, for achieving substantemperature balance as high as possible, i.e., a low temperature drop over the entire roller surface. The equalized temperature is necessary in order to avoid undesirable different properties of the treated materials over the web width. Examples thereofare the varying drying degree when drying paper webs and the varying mechanical properties over the web width during heating and cooling in the manufacture of synthetic plastic films.

Sufficient tests have been carried out to construct heatable or coolable rollers by means'of which a surface temperature as uniform as possible can be achieved.

The simplest known constructions are roller constructions in which a heating or cooling medium can be fed via a hollow roller projection in the middle of the end wall through a stationary tube and also returned there. Drawing-off also can be performed on the opposite side or on both sides. In each case, a longitudinal flow is developed in the rollers, which is directed towards the one or the other roller end or from the middle of the roller towards both roller ends.

By heat emission or heat absorption, the flow of a liquid, however, involves a temperature drop or rise, which necessarily leads to an unequalized temperature over the roller surface. This temperature gradient'can be maintained low by means of large quantities of liquid, but would achieve a value of zero only with an infinitely large throughput of liquid. Using larger quantities of liquid, however, is considerably limited in practice for technical reasons and since it would be necessary to use technically expensive equipment. Another drawback is that the described constructions are uneconomical.

When a roller is not heated by means of a liquid but by means of vapor blow in without the application of superat mospheric pressure, i.e. with the use of water vapor as the heat carrier to temperatures up to a maximum of 100 C., the problem of achieving a uniform temperature is even greater since the vapor is condensed partially on the roller wall and partially in the lower portion of the roller to form a pool. Even when the vapor is uniformly distributed over the roller length, a substantial temperature gradient occurs, which changes in dependence upon the quantity of vapor employed.

In the case of other roller constructions, heating or cooling coils or several adjacent tubes incorporated in the roller bodies and distributed over the circumferences thereof are used, but balanced surface temperatures cannot be achieved with these constructions either, since a temperature gradient always is caused in the direction of flow.

In US. Pat. Nos. 1,820,074, 2,015,747, and in French Pat. N'o. 434,455, rollers are disclosed having concentric displacement bodies incorporated in the roller bodies, the outside diameter of which is only slightly smaller than the inside diameter of the roller bodies. A narrower flow cross section is achieved by means of which high flow speeds can be achieved and the already high heat transfer can be further improved thereby. The formation of a temperature gradient along the flow direction can not be avoided by means of these constructions, however. I I

A modification of the described roller constructions is disclosed in German Pat. No. 1,178,201, which describes a heatable or coolable roller for calenders or rolling mills in which the displacement body has a conical shape, the diame ter increasing in the direction of flow of the heating medium. By means of the decrease of the flow cross section and the increase in the flow speed thereby caused in the direction of flow, the unavoidable temperature drop is equalized by the heat transfer also increasing with the increasing flow speed. Since, however, the temperature drop of the heating medium desired temperature balance can not be realized with changing conditions in practice, e.g., the changing humidity of the dry goods and the change of the absolute roller temperature.

The journal Das Papier," 21st year, No. 10, 1967, describes another roller construction in which the heating or cooling liquids are rotated at a high speed in the interior of the roller by means of an axial pump impeller driven from the outside. Temperature variations on the roller surface are avoided by sufficiently large rotated quantities with this construction, but the outside drive of the pump impeller is expensive and requires additional equipment.

The problem is to provide a heatable or coolable roller which does not have the drawbacks and disadvantages of the described constructions and by means of which an optimum temperature balance on the roller surface can be achieved by intensively rotating the heating or cooling medium in the interior of the roller.

The present invention provides a heatable or coolable roller in the form of an outer hollow cylinder, which is mounted on one or both sides in hollow shafis, through which a heating or cooling medium enters and/or leaves via a pipe conducted through the hollow shaft, and which contains in the interior thereof a circulating device for the heating or cooling medium. The circulating device of the roller consists of a coaxial hollow cylinder, or two coaxial hollow cylinders having a space between them, being fixed to the ends of the outer holupon the flow speed, follows an exponential function, the

low cylinder, acting as conducting elements, carrying feeding elements causing flow, and having openings for the flowing medium adjacent the ends thereof. The feedpipe has outlets, preferably positioned at the same distance from the middle of the roller, for feeding the heating or cooling medium.

When the roller is rotated, an intensive and continuous circulation of the heating or cooling medium is achieved in the roller by means of the circulating device rigidly connected with the outer hollow cylinder of the roller, an equalized surface temperature being obtainable thereby even on the surface of long rollers without substantial additional equipment, such additional driving means.

When the roller is rotated, the heating or colling medium, e.g. water, vapor, oil, or the like, is fed via a feedpipe passing through a hollow roller projection in the middle of the end wall of the roller and leaves at the bores of the feedpipe. During rotation of the roller, the liquid pool is contacted by the hollow cylinders provided with the feeding elements and displaced in the direction of the longitudinal roller axis. If the cir-' culating device consists'of one hollow cylinder extending over the entire roller length, the medium is displaced over the entire roller length in one direction through the space between the outside and the inside hollow cylinders. At the end of the roller, the medium flows through the openings and back in the interior of the inside hollow cylinder and via the openings at the opposite end again into the space between the circulating device and the exterior hollow cylinder.

In another embodiment, two identical inner hollow cylinders are mounted with a space between them.

The discharge of the heating or cooling medium is perrefined by means of a hollow shaft, either the same hollow shaft through which the feedpipe is conducted or another hollow shaft mounted at the opposite end of the roller being used.

The feeding elements may be inclined blades which should be so distributed over the circumference of the hollow cylinder that the requirement of a continuous flow is fulfilled.

In a preferred embodiment, the feeding elements are screw helices since their feeding quantity per roller revolution can be predetermined very accurately and their manufacture is particularly simple.

The direction in which the medium flows to-and-fro depends upon the direction of rotation of the roller and the pitch direction of the feeding elements. The feeding elements may have the same pitch directions, a to-and-fro flow direction being produced thereby. This kind of arrangement, however, is preferred in a circulating apparatus consisting of a single internal hollow cylinder.

When employing two internal hollow cylinders, the feeding elements preferably have two opposite pitch directions. This results in oppositely directed circulation flows towards the middle of the roller. The advantage of such an arrangement is that the circulation is divided into two partial flows which again mix in the middle of the roller.

Despite the fact that there is a certain tolerance in deter mining the cross-sectional surface of the circulating device, with respect to that of the roller, i.e. of the outer hollow cylinder, it has been found in practice that best results regarding low-loss flow with minimum pumping are achieved when the cross-sectional surfaces for both flow directions are identical or almost identical.

Similar, as described above, is the relation between the cross sections of the openings and the cross section of the circulating device. Although a certain variation is possible in this relation, rollers with openings having a total cross-sectional surface at least equal to the cross-sectional surface of the interior shell have proved particularly suitable.

If the circulating device consists of two inner hollow cylinders, these are spaced from each other. The two partial flows mix in the space between hollow cylinders if the hollow cylinders are provided with feeding elements producing countercurrent flows. In order to achieve minimum deviation losses, the space between the hollow cylinders preferably is so selected that the cross section of the opening between the inner hollow cylinders is at least equal to the total cross section of the openings.

In a preferred embodiment, especially in the mounting of two inner hollow cylinders, the bores of the feedpipe through which the heating or cooling medium enters into the roller have the same distance from the middle of the roller, in order to achieve a substantially uniform distribution during feeding of the medium. In this case, the number of the bores is not limited, but more than two are preferred. In another embodiment, identical bores are mounted for the above reasons, the cross sections of which are small with respect to the cross section of the feedpipe. Advantageously, especially with the use of vapor, the bores are directed downwardly in order to achieve immediate mixing with the circulating medium.

For decreasing the flow resistance, a roller construction containing two spaced inner hollow cylinders has guide elements, especially in the form of inclined, straight, or bent surfaces.

EXAMPLE When the feeding elements of the circulating device are in the form of screw helices, the circulating device, in its type of apparatus, corresponds to a screw pump.

The theoretical discharge V of a screw pump is D,, is the outside diameter of the screw helices D, is the inside diameter of the screw helices s is the pitch of the screw helices n is the number or revolutions of the screw helices.

The outer hollow cylinder of the roller selected for the exemplary embodiment had an outside diameter of 450 mm. and an inside diameter of 400 mm. The outside diameter of the helices was 398 mm. and the inside diameter 280 mm. The pitch of the helices was 500 mm.

The theoretical discharge of a roller filled to 45 percent of capacity thus is V==0.45-(1r/4) (39.8 -28)-50-n =14,200-n(cm. /revolution)=I4.2-n(dm. /revolution) With a number of roller revolutions of n= r.p.m. =1 ,200 r.p.hr., the circulated liquid quantity V=l4.2'l ,200=l7,000 dm.-"/hr.= l 7.0 mil hr.

In a construction including two inner hollow cylinders, the discharge thus is 34 mP/hr.

The actual discharge is somewhat smaller than the theoretically calculated quantity. It is decreased, for example, with an increase in the gap between the helix and the inside diameter of the roller body and increased by higher flow resistances corresponding to the lift of the pump. In practice, the gap is maintained as small as possible. In this example, it was 1 mm., as can be seen from the above data.

The flow resistances are relatively low but in a special embodiment they may be still further decreased by lowering the deviation resistance. This is performed, for example, by guide elements in the middle of the roller employing two inner hollow cylinders or by a suitable design, e.g. a conical configuration, of the front surfaces at the inner side of the roller.

The output required of the pump is very low so that the roller of the invention is also employed as a free-running, i.e., undriven, roller, the pump output being produced by the web of material passing over the roller. With an average lift of 0.1 m. corresponding to the flow resistance, the power necessary for circulating 34 mP/hr. was 9.3 watts only.

By feeding a heating liquid in a quantity of l m. /hr., the liquid pool was circulated about 30 times, in the case of two inner hollow cylinders.

With a roller rotated at r.p.m.-6,000 r.p.hr. (such rollers are employed, for example, in the drying of paper or film webs)the circulated quantity was about m."/hr.. i.e., 150 times the feed, and removed a quantity of liquid of I m./hr.

When feeding and removing 20,000 thermal units in the case of a roller without circulating devices, the calculatable temperature drop over the roller length amounts to 20 C. with a liquid throughput of l mFIhr. When circulating 30 m. /hr., the temperature drop is decreased to 067 C., and when circulating 100 m. /hr., to 0.2 C.

When circulating n times the feed quantity of heating or cooling medium, the temperature drop generally is decreased, with respect to a roller without a circulating device, to a value of l/n, i.e., in the case of a roller circulating the liquid pool 30 times, to 3 percent.

The accompanying drawings illustrate some roller constructions but the invention is not restricted to the illustrated embodiments.

FIGS. 1 to 3 are views, in longitudinal section, showing three different embodiments of the roller of the invention, and

FIGS. 4 and 5 are views in elevation of two types of circulating devices.

FIG. 1 is a section through a roller having as the circulating device an inner hollow cylinder 5 which is rigidly connected with the outer hollow cylinder 1 at the end walls 2. On the inner hollow cylinder, having openings 7 towards the ends, there is the feeding element 6. Feeding and discharge of the heating or cooling medium is performed via one of the hollow roller projections in the middle of the end wall through which the feedpipe 4 is conducted. The medium enters the interior of the roller via the bores 8.

FIG. 2 is a section through a roller which has, as the circulating device, two inner hollow cylinders 50 and 5b having a space a between each other. The feeding elements 6a and 6!; have opposite pitches. The bores 80 and 8b of the feedpipe 4 are positioned at the same distance from the middle of the roller.

FIG. 3 is a section through a roller which has guide elements 9 mounted between both inner hollow cylinders 50 and 512 for diminishing the deviation resistances. The inner sides of both end walls 2 have a substantially conical shape. The bores 80 and 8b of the feedpipe 4 are positioned at the same distance from the middle of the roller.

FIG. 4 shows an internal body 5 in which the feeding element 6 is a screw helix.

FIG. 5 shows an internal body 5 in which the feeding elements 6 are inclined planar surfaces.

It will be obvious to those skilled in the art that many modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications.

What is claimed is:

l. A heatable or coolable roller which comprises a hollow cylindrical exterior shell, at least one hollow cylindrical interior shell secured to the exterior shell and having aperture means therein adjacent each end thereof, flow-causing means on the exterior of the interior shell for causing circulation of a heat transfer medium around the interior shell, and means for introducing heat transfer medium into said roller and discharging said medium from said roller.

2. A roller according to claim 1 including two hollow cylindrical interiorshells having a space between them, each shell having aperture means therein adjacent one end and opening means at the other end.

3. A roller according to claim 1 in which the flow-causing means is a helical rib.

4. A roller according to claim 1 in which the flow-causing means is a plurality of blades inclined with respect to the roller axis.

5. A roller according to claim 1 in which the cross-sectional area of the interior shell is about equal to half the cross-sectional area of the exterior shell.

6. A roller according to claim 1 in which the aperture means in the interior shell have a total cross-sectional area at least equal to the cross-sectional area of the interior shell.

7. A roller according to claim 1 in which the means for introducing heat transfer medium into the roller includes a feedpipe having downwardly directed bores thereinv 8. A roller according to claim 2 in which each interior shell has flow-causing means thereon pitched in the same direction.

9. A roller according to claim 2 in which each interior shell has flow-causing means thereon pitched in opposite directions.

10. A roller according to claim 2 in which the space between'the inner hollow cylinders is so selected that the cross section of the opening between the inner hollow cylinders is at least equal to the total cross section of the openings.

11. A roller according to claim 2 including guide means between the two inner hollow cylinders. 

1. A heatable or coolable roller which comprises a hollow cylindrical exterior shell, at least one hollow cylindrical interior shell secured to the exterior shell and having aperture means therein adjacent each end thereof, flow-causing means on the exterior of the interior shell for causing circulation of a heat transfer medium around the interior shell, and means for introducing heat transfer medium into said roller and discharging said medium from said roller.
 2. A roller according to claim 1 including two hollow cylindrical interior shells having a space between them, each shell having aperture means therein adjacent one end and opening means at the other end.
 3. A roller according to claim 1 in which the flow-causing means is a helical rib.
 4. A roller according to claim 1 in which the flow-causing means is a plurality of blades inclined with respect to the roller axis.
 5. A roller according to claim 1 in which the cross-sectional area of the interior shell is about equal to half the cross-sectional area of the exterior shell.
 6. A roller according to claim 1 in which the aperture means in the interior shell have a total cross-sectional area at least equal to the cross-sectional area of the interior shell.
 7. A roller according to claim 1 in which the means for introducing heat transfer medium into the roller includes a feedpipe having downwardly directed bores therein.
 8. A roller according to claim 2 in which each interior shell has flow-causing means thereon pitched in the same direction.
 9. A roller according to claim 2 in which each interior shell has flow-causing means thereon pitched in opposite directions.
 10. A roller according to claim 2 in which the space between the inner hollow cylinders is so selected that the cross section of the opening between the inner hollow cylinders is at least equal to the total cross section of the openings.
 11. A roller according to cLaim 2 including guide means between the two inner hollow cylinders. 